Automatic headlight control



July 3, 1951 D. B. LE CROY 2,558,969

AUTOMATIC HEADLIGHT CONTROL Filed May 6, 1949 IN VEN TOR.

A/TTORNEYS.

Patented July 3, 1951 UNITED STATES PATENT OFFICE 9 Claims. 1

My invention relates to an improved mechanism for automatically dimming the headlights of an automobile or the like in response to the lights of an approaching vehicle, and holding them in a dimmed condition for a predetermined time.

This application is a continuation in part of the copending application of myself and William B. Rood, entitled Electronic Headlight Control, S. N. 4,437, filed January 26, 1948 now abandoned.

One of the problems associated with modern high intensity automobile lights arises from the blinding efiect of these lights on the drivers of approaching cars and the consequent danger of accident if the operator of a car overlooks the necessity of dimming his lights.

In accordance with the present invention an improved automatic mechanism operative to dim automobile headlights or the like in response to the approach of an oncoming car is provided. The lights are automatically sealed in the dim condition and held in that condition for a fixed time, such as 3 seconds, suiiicient for oncoming vehicles to pass. The time period also avoids unnecessary cycling of the mechanism when a string of cars is passed.

It is therefore a general object of the present invention to provide an improved automatic headlight dimming mechanism.

Another object of the present invention is to provide an improved headlight dimmer operable to hold the headlights in the dim condition for a predetermined fixed time regardless of the intensity of the oncoming illumination.

Yet another object of the present invention is to provide an improved headlight dimmer having a simple and inexpensive electrical circuit draw ing only a small current.

A further object of the present invention is to provide an improved headlight dimmer that positively seals in the dim or bright condition in reresponse to incident illumination.

Still another object of the present invention is to provide an improved headlight dimmer having means manually operable at all times to overrule the automatic mechanism.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, as well as further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure l is a circuit diagram of a headlight dimmer constructed in accordance with the present invention; and having manual means operable at all times to turn on the high beam;

Figure 2 is a circuit diagram of an alternative embodiment of the dimmer circuit of Figure 1, having manual means operable at all times to turn on the low beam; and,

Figure 3 is a circuit diagram of an alternative embodiment of the dimmer of the circuit of Figure 1, having no manually operable means to overrule the automatic mechanism.

Referring now to Figure 1, there is shown at 10 a photomultiplier tube, such as a type 931A, having an electron-emitting cathode Ilia, a plurality of multiplying electrodes or dynodes 10b, and an anode I00. This tube is mounted in a suitable housing on the left front fender of the automobile or some other suitable location so that the lights of oncoming cars illuminate the cathode Illa and cause electron emission from the same. The electrons so emited travel to and strike the closest multiplying electrode illa where they produce many more secondary electrons which in turn travel to the adjacent electrode we where the next step in the multiplying process takes place. This process continues until the electron. train reaches anode I00, the total number of electrons at this time being far in excess of that emitted by cathode [0a.

The cathode lfla is maintained at approximately 850 volts negative relative to ground by means described hereafter. This voltage is uniformly distributed among the multiplier electrodes [0b by the resistors [2 which may, for example, be 47,000 ohms each.

The last multiplier electrode lllb is connected to ground through variable resistor [4 which may, for example, be 300,000 ohms. This resistor controls the sensitivity of the circuit to oncoming lights by controlling the voltage step between each pair of adjacent multiplying electrodes illb.

The anode of tube I0 is connected through shielded wire 16 to the control electrodes 18a of the electron tube l8 which may, for example, be a 6SN'7 tube. Resistance 20 defines a current path to ground from control electrodes Ba and may be approximately 10 megohms.

The current path through tube I!) may be traced from filter capacitor 22 to cathode lfla, through tube I0 to anode I00, through cable l6, and through resistance 20 back to capacitor 22. Since the anode of tube We is positive relative to the cathode 10a, increase in this current flow renders the control electrodes iiia more negative and thereby reduces current flow in tube i8.

Tube l8 controls the operation of the relay defined by actuating coil 24 and normally open contacts 24a. The current path through this tube may be traced from the cathodes I81) to the cathode resistance 25, through portion 28a of the secondary winding of transformer 28, through coil 24, to the anodes I80 of tube [8. Since the energizing coil of relay 24 is in this current path, this relay drops out when the negative potential on control electrodes l8a exceeds a predetermined value.

Resistance 26 may be approximately 1600 ohms.

A capacitor 3% of approximately 4 microfarads is connected across coil 24 to maintain constant current therethrough and prevent contact chatter due to the intermittent current fiow through tube IS.

The relay contacts 24a in turn energize (or deenergize) the low voltage relay 36. This relay is defined by the energizing winding 30a, the normally open contacts 3% and the normally closed contacts 330. The energizing circuit for relay 30 may be traced from the car battery 32 to main switch 34, pole 36a, of polarity reversing switch 36, winding 30a, contacts 24a of relay 24, and through pole 35b of switch 36 back to ground.

The headlight bulbs are indicated at 38, each having a dim or low filament 38b and a bright or high filament 380.

In the unenergized condition of relay 3%, the switch 30c is closed and the dim or low filaments 38b are energized by the circuit which. may be traced from battery 32 through switch 34, contacts 30c, switch 40, to filaments 38b and through these filaments to ground.

When relay 30 is energized, the contacts 3022 close to define a direct circuit from switch 34 to the high or bright filaments 380.

Since the contacts 24a are held in the closed condition by current flow through tube l8, and that current flow decreases with illumination on phototube H], the dim or low filaments 380 are energized when the light on cathode Illa reaches a predetermined intensity.

Space path voltages for tubes [0 and i8 are derived from vibrator 42 which alternately energizes the two halves of primary 2% of transformer 28. The resulting alternating voltage induced in portion 280, of the secondary winding of that transformer is applied directly to tube i8 which acts as a rectifier to draw current only in one direction through energizing coil 24.

The full voltage induced in secondaries 28a and I 280 is applied to capacitor 22. The phototube [0 acts as a rectifier in conjunction with this capacitor to charge it to a potential suitable for operation of that tube.

The automatic control is turned on and off by switch 44 which interrupts the circuit from battery 32 to vibrator 42 and the filament of tube !8.

Indicator light 46 is energized when either the dim or the bright beams are on. This operation results from the circuit which can be traced from switch 34, through contacts 313b, to lamp 46 and from that lamp through switch to the unenergized high beam filaments 3317. Since the latter are unenergized, they have no significant voltage drop and the lamp 46 receives practically full battery voltage. When the bright or high beam goes on, the lamp 46 is energized through contacts;30c and the unenergized low or dim. filaments 330.

4 single pole double-throw switch operative to energize the filaments respectively. The lamp 46 is connected across the two fixed terminals of this switch.

The manually operated double-throw switch 40 operates to overrule the automatic mechanism and to switch on the high beam filaments 380. For this operation, it is switched to the position of the dotted lines of Figure 1 and to define a circuit to the high or bright filaments 38c irrespective of the condition of relay 30. This results from the fact that this switch defines a circuit from the contacts 30c to the high filaments 38c and interrupts the circuit to the low filaments 3817.

In accordance with the present invention, the

relay 3i] is sealed in the open position for a fixed period of about 3 seconds after each operation. This sealing is efiected by capacitor 48 which is connected from winding 3% to the control electrodes lea of tube It.

The charging and discharging circuit for capacitor 48 may be traced from ground to resistance 28, to capacitor 48, through switch 240. or winding 30a back to ground, either directly through switch 36 or through battery 32. Capacitor 4 8 is about 0.05 microfarad to give a time constant of about 0.5 second.

When the space current fiow in tube I8 is reduced by light incident on tube Hi to a valve opening relay 24, the switch 2% suddenly opens and the current how in winding 36a is suddenly cut off. This high rate of current change in winding 39a produces a large positive Voltage at the common terminal of that winding and condenser 48 to impart a fixed charge thereto which iases the control electrodes !8a of tube It. to a fixed negative potential when the current change in winding 30a ceases. The current flow in tube 58 is thereby maintained at a value insufficient to energize relay winding 24 for the fixed period required for capacitor 48 to discharge.

Since the value of the charge on capacitor 48 is determined :by the operation of contacts 24a and not by the intensity of illumination on tube it, the time delay is uninfiuenced by the illumination intensity. In other words, once the threshold value is exceeded, the capacitor 48 is fully charged and the predetermined time delay period started.

The purpose of polarity reversing switch 36 is to control the direction of current fiow through winding 3M to give the requisite polarity of charge on capacitor 48. If the polarity is wrong, the unit cycles from one condition to the other at a period of approximately 3.5 seconds.

When the charge on capacitor 43 leaks off through resistance 28 to the value at which relay 24 is deenergized and contacts 24a close, a. reverse surge occurs through capacitor 48 to raise the potential of control electrodes iiia and positively deenergize relay 24.

A capacitor may be connected across the cathode resistance 26 although this is not necessary for efiecti've operation.

The relay 24 is adapted to close contacts 24a upon current flow of about 3 milliamperes. It opens these contacts when the current is subsequently reduced to about 2.2 milliamperes The winding 39a has an impedance of approximately 7,000 ohms at cycles per second frequency. I

The circuit of Figure 2 is like the circuit of Figure 1 except that operation of manual switch 453 overrules the automatic mechanism to energize the dim or low filaments 3812. It will be observed that when this switch is in the position of the dotted lines the contacts 35b and 390 define parallel paths from filaments 38b to battery 32. The box 48 diagrammatically represents the portions of the automatic control unit not shown in detail in Figure 2.

"In the circuit of Figure 3, the switch t is eliminated so that no manual overruling of the automatic mechanism is provided.

It will be observed that the mechanism of Figure 1 operates to switch lamps 38 to the dim or low beam when the voltage between cathodes l8b and control electrodes 18a exceeds a predetermined value corresponding to the threshold illumination of phototube ill. These electrodes thus define terminals across which the control voltage is impressed. The capacitor 48. impresses voltage across these terminals by reason of its direct connection to the control electrodes l8a and its connection to the cathodes '81) through winding 38a, ground, and cathode resistance 25. The latter circuit also includes battery 32 in one setting of switch 36. Resistance 2E1 defines a discharge path for capacitor 48.

The contacts 302; and 30c combine to define a single pole-double throw switch to energize the low and high filaments respectively. In other words, these contacts selectively establish a conducting path from their common connection or terminal to one or the other of the terminals connected to the lamp filaments.

While I have shown and described particular embodiments of my invention it will, of course. be understood that I do not wish to be limited thereto and intend by the appended claims to cover all modifications and alternative constructions as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a dimmer for headlights of the having an electron tube with cathode cont ol electrodes, and means including a relay winding operable to dim the headlights when the cathode to control electrode voltage of said tube exceeds a fixed value. the improvement comprising a capacitor connected to impress voltage between said cathode and control electrode, means definin an electric circuit from said winding to said condenser to charge said condenser upon a sudden current change in said winding and means defining a discharge path for said capacitor.

2. In a headlight dimmer, an electron tube having cathode and control electrodes. a relay having a winding operative to dim said headlights in accord with its state of energization, means operative suddenly to change the energization of said relay in accord with the current fiow in said tube, a capacitor connected to impress voltage between said control electrode and said cathode, means defining an electric circuit from said winding to said control electrode, and means defining a discharge path for said capacitor.

3. A dimmer for headlights comprising in combination, a relay having a winding and adapte: when energized to dim said headlights, a second relay having a pair of contacts adapted to close when voltage across a pair of terminals exceeds a predetermined value, means defining an energizing circuit for said first winding through contacts, a capacitor, means defining a series circuit through said capacitor and said winding to said pair of terminals and means defining a discharge path across said terminals.

l. A headlight control comprising in combination, an electron tube having cathode and control electrodes, means responsive to incident light to bias said electrodes relative to each other, a relay having an energizing winding and operative to control said headlights when energized, means suddenly to change the state of energization of said winding when said bias exceeds a predetermined value, a capacitor connectedto impress voltage across said electrodes, means defining an electric circuit from said winding to said capacitor to charge said capacitor when the state of energization of said Winding is changed, and means defining a discharge path for said capacitor.

5. A control circuit adapted to produce fixed time delay regardless of the extent voltage across a pair of terminals exceeds a predetermined threshold value, said circuit including an inductive element, means suddenly to change the current flow through said element when said voltage exceeds said threshold value, a capacitor connected to impress voltage across said terminals and means connecting said capacitor to said element to impress a predetermined charge on said capacitor when said current change occurs.

6. A control circuit adapted to produce a fixed time delay regardless of the extent the voltage across a pair of terminals exceeds a threshold value, said circuit including an inductive element, means responsive to said voltage and operative to cut off predetermined current flow through said element when said voltage exceeds threshold level, a capacitor connected to im press voltage across said terminals, and means connecting said capacitor to said element to impress predetermined charge on said capacitor when said current flow is cut off.

'7. A control circuit adapted to produce a fixed time delay regardless of the extent the voltage across a pair of terminals exceeds a threshold value, said circuit including a relay having a winding, means defining an energizing circuit to said winding, elements adapted suddenly to interrupt said circuit when said voltage exceeds said threshold value, a capacitor connected to impress voltage across said terminals, and means connecting said capacitor to said winding to impress a predetermined charge on said capacitor when said voltage exceeds said threshold value.

8. A control circuit adapted to produce a fixed time delay regardless of the extent voltage across a pair of terminals exceeds a threshold value, said circuit including a relay having a winding, means defining an energizing circuit to said winding, elements adapted suddenly to interrupt said circuit when said voltage exceeds said threshold value, a capacitor and a resistance connected across said relay coil, whereby said capacitor receives a fixed charge when said circuit is interrupted, and means to impress voltage across said terminals in accord with the charge on said capacitor.

9. A control circuit adapted to produce a response for a fixed time period after voltage across a pair of terminals exceeds a predetermined threshold value regardless of the extent the threshold value is exceeded, said circuit including an inductive element, means to produce current flow through said element, means responsive to the voltage across the terminals operative to cut off current flow through the element when the threshold level is exceeded, a capacitor, means 7 defining a circuit to impress voltage from the capacitor across the terminals, means connecting the capacitor to the element to impress a predetermined charge on the capacitor when said current flow is cut off, and means operative in re- -5 sponse to the charge.

DONALD B. LE CROY.

REFERENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS Number Name Date Alley Mar. 21,1939 Berg, Jr. Oct. 29, 1940 Friedman Nov. 25, 1947 Schmidt, Jr. July 19, 1949 Moore et a1. Jan. 3, 1950 

